Surveying poles are topographic instruments used to measure different geographic parameters, such as point positions on the ground, distances as well as angles. Typical applications are position survey markets, buildings, road construction and mapping. Recently, the classical mirror-based surveying pole used for topographic surveying works in outdoor environments has been replaced by GNSS based poles which rely on the aid of the global navigation satellite system GNSS, like the Trimble R8. FIG. 1 depicts a GNSS-based pole 100 which comprises a rod 110 with a bottom end 120 for positioning on a point 140 on the ground which needs to be localized. The top end 130 comprises a GNSS device for determining the geographical coordinates of the GNSS antenna reference point 150. When the pole is completely vertical, the difference in coordinates between the ground point 140 and the GNSS point 150 is equivalent to the height of the pole 160 (approximately the length of the rod). GNSS-based poles are easier to operate because they do not need external equipment for making further measurements as all GNSS electronics are contained within the GNSS device. They also provide fast position computation and, thus a faster topographic survey, than traditional mirror-based systems.
The theoretical basis underlying the surveying pole is to first compute the GNSS antenna position 150 through a geodetic GNSS receiver and subsequently project the point to the ground taking into account the height difference 160. The operation is performed by a user that handles the surveying pole, placing the bottom end 120 on a desired ground point 140 for obtaining its 3D position coordinates. The main drawback is that the pole needs to be completely vertical, therefore it is necessary to level the pole using a level. This requires further handling, takes more time, and can lead to errors.
Unfortunately, even if an excellent verticality is achieved, there are situations that do not allow placing the pole in the required vertical position, and thus, the use of such poles is not possible. Such situations could be due to obstacles, for example, inside or around buildings, tunnel entrances or trees. FIG. 2 depicts such situations, wherein a tree 220 or building 230 obstructs (represented by the cross) the direct line-of-sight between the GNSS device and the satellite system 210.
Surveying pole solutions exist which attempt to solve this problem by allowing the pole to be tilted for determining the ground point coordinates both in vertical and oblique mode. The capability of tilting the pole has the advantage of measuring points that were otherwise inaccessible, like in environmental conditions where a full visibility of the sky is not possible, such as areas obstructed by trees, inside buildings or other obstacle objects. Also, by tilting the pole, it is possible to have a direct line of sight to more satellites than otherwise, and hence a more precise ground point position can be determined.
However, in order to properly perform the ground point projection, the attitude, or orientation, of the tilted pole needs to be determined in order to determine the actual vertical difference between the top and bottom ends of the pole. Thus it is necessary to include additional hardware sensors to measure this pole orientation and compensate for the vertical height difference due to the pole being tilted.
FIG. 3 depicts the three rotation angles defining the attitude, or orientation, of a surveying pole. The first angle θ, the heading or yaw, is the angle which defines a rotation around the vertical z-axis 310. When the pole is pointing north, the heading is zero, however by rotating the pole clockwise or counter-clockwise, a heading is generated. The second angle α, the pitch, is the angle which defines a rotation around the horizontal y-axis 320. When the pole is completely vertical, the pitch is zero, however by moving the pole forward or backward, a pitch is generated. The third angle (3, the roll, is the angle which defines a rotation around the horizontal x-axis 330. When the pole is completely vertical, the roll is zero, however by moving the pole right or left, a roll is generated.
Current GNSS tilt surveying pole solutions estimate the orientation of the pole using magnetometers and inclinometers, like the Trimble R10, necessary to perform GNSS positioning at an angle. FIG. 4 depicts a surveying pole 400 comprising the additional magnetometer and inclinometer components within the GNSS device 410. By using the magnetometer, it is possible to obtain the pole orientation in relation to the magnetic North, that is, the heading. With the use of two orthogonal inclinometers it is possible to determine the remaining two tilt angles (pitch and roll) of the pole in relation to the vertical axis respect to ground. Hence, this solution allows working in tilted mode as all three angles are obtained using a magnetometer and inclinometer.
However, such solutions suffer from critical restrictions due mainly to interference caused by environmental magnetic fields. The strongest electromagnetic fields found in such scenarios are generated by electromagnetic induction, such as existent near railways, electric power stations or near metallic objects, which are typically construction environments where topographical surveys need to be conducted. The electromagnetic fields of the surroundings affect the measurements as these traditional poles sense the magnetic field of the Earth and the measurements are distorted by this interference field, resulting in errors in attitude determination, as well as inaccurate topographical surveys.
Therefore a need exists to effectively solve the abovementioned problems.